This invention relates to paper feeding apparatus such as a paper feeding means for an automatic document feeder attached to a recording apparatus for an electrophotographic copying machine or an image reading apparatus, a paper feeding cassette, a paper feeding means for feeding paper sheets from a paper feeding apparatus with large capacity, and a paper refeeding apparatus for feeding paper sheets having been subjected to recording from a stacker for recording on the reverse sides.
Each of the above-mentioned paper feeding means separates and feeds a sheet of paper from a paper feed tray (stacking tray) receiving a plurality of paper sheets to next process.
An automatic document feeder, for example, is composed of a paper feed tray, paper feeding means, transport means, and paper discharging means. The paper feed tray is composed of a document carrying stage for carrying a plurality of document sheets and a movable width regulating plate for aligning the side edges of document sheets. The paper feeding means separate a sheet out of the stack of the document sheets placed on the paper feed tray and feed it to an image reading portion on a document placing board (glass platen). The transport means transport, with an endless belt or a roller provided rotatably on the glass platen, the document sheet fed onto the upper side of said glass platen along its surface to a predetermined position, where it is stopped and later conveyed out by the transport means after its image being read. The paper discharging means eject the document sheet thus conveyed out from the transport means onto an exit tray or the paper feed tray, or invert the document sheet conveyed out from the transport means upside down and transport it onto the glass platen again, where it is subjected to the reading of the image on its reverse side.
A paper feeding apparatus of the type such as to separate and feed a paper sheet out of sheets of paper carried on a paper feed tray for carrying paper sheets is composed of (1) conveying-out means made up of a pick up roller for conveying out the paper sheets carried on the paper feed tray and a movable pressing plate, (2) separating means made up of a feed roller and a reverse roller (separation roller) for separating the sheets of paper conveyed out by said conveying-out means to pick up one for feeding, (3) a pair of registration rollers for adjusting the posture of the paper sheet separated and conveyed by said separating means, making it to be in a ready state, and feeding it again in response to a re-feeding signal, (4) drive means for driving each of these means, and (5) control means for controlling the driving of said drive means.
The paper feeding apparatus having above-mentioned composition has following subjects to be solved.
(1) In the paper feeding operation in the above-mentioned paper feeding apparatus, the paper sheet conveyed by the aforesaid conveying-out means and separating means reaches the pair of registration rollers to contact with the outer surface, where it is corrected for its skew to be in ready position, then in response to the re-starting signal the pair of registration rollers rotate to feed it again.
Regarding this operation for correcting the skew of the paper sheet, it has been heretofore carried out with an electromagnetic clutch the switching operation between stop and normal rotation of the registration roller pair. This switching with an electromagnetic clutch has such problems that (1) the apparatus is made to be of high manufacturing cost due to the use of a high-cost electromagnetic clutch, (2) when being actuated, the electromagnetic clutch generates noises such as shock noise etc., (3) the position of stopping of the document sheet conveyed onto the glass platen by the rotation of the pair of registration rollers is uncertain, and so forth.
(2) In the paper feeding apparatus of prior art, the movable pressing plate for pressing the pick-up roller in the conveying-out means presses the roller until the leading edge of the conveyed paper sheet reaches the nip position of the feed roller and the reverse roller in the separating means. However, in some cases the feeding operation of the feed roller is less effective than the reversing operation of the reverse roller, whereby the leading edge of the paper sheet does not reach the pair of registration rollers, resulting in failure of paper feeding.
(3) On condition that the peripheral speed of the pick-up roller and that of the feed roller are equal, the paper sheet extended between the pick-up roller and the feed roller becomes a load to the feed roller, which makes the separation and feeding of paper sheets unreliable.
(4) When the pair of registration rollers rotate to feed the paper sheet, if the reverse roller rotates at the same time by the reverse rotating drive of the drive motor, sometimes the paper sheet is made to get back with its leading edge made apart from the nip position of the registration rollers, resulting in no feeding by the registration rollers, which makes the cause of the paper feeding failure.
(5) The drive motor for driving the movable pressing plate to move up and down in the conveying-out means of prior art is fixed directly to the paper feeding apparatus mainframe with screws and the like, hence when said drive motor is driven to rotate normally or reversely, the vibration generated in the drive motor due to rotation is transmitted to the paper feeding apparatus mainframe where an abnormal noise is generated.
(6) If a buffer member is fitted in the mounting portion of the supporting member for holding the drive motor in order to prevent this abnormal noise, it increases the number of component parts to make the manufacturing cost higher.
(7) In the paper feeding operation in the above-mentioned paper feeding apparatus, a preceding paper conveyed by said conveying-out means and separating means is transported by the normally rotating pair of registration rollers to the next processing station, and upon passing of its trailing edge through the nip position (P.sub.2 point) of the feed roller and the reverse roller, the feed roller is driven to rotate reversely by the reverse rotation of the reverse roller pressing the feed roller, and at the same time, the pick-up roller which is connected to this reverse roller with a belt is also driven in the reverse way to give a force acting on the following paper sheet to get back to the upstream side of feeding. In case of a considerable number of paper sheets to be fed, sometimes the reverse rotation of the reverse roller and the feed roller makes the following sheets get back to the upstream side of the feeding to such a degree, that the leading edge of the paper sheets are transferred to the upstream side apart from the feeding pressure point (P.sub.1 point) where the pick-up roller is pressed by the movable pressing plate, resulting in the impossibility for the following paper sheet to be conveyed.
(8) In the paper feeding apparatus of prior art, a small number of sheets out of a large number of sheets is conveyed out, by the normal rotation drive of the feed roller and the pressing force of the movable pressing plate in the conveying-out means, to the press-contact point of the feed roller and the reverse roller, however, in the case where a paper sheet with a large curl is conveyed, sometimes the leading edge of the paper sheet does not reach the nip position of the feed roller and the reverse roller so long as only the pick-up roller is employed, resulting in paper feeding failure.